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  The Mesa 3D Graphics Library
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<h1>Coding Style</h1>

<p>
Mesa is over 20 years old and the coding style has evolved over time.
Some old parts use a style that's a bit out of date.

Different sections of mesa can use different coding style as set in the local
EditorConfig (.editorconfig) and/or Emacs (.dir-locals.el) file.

Alternatively the following is applicable.

If the guidelines below don't cover something, try following the format of
existing, neighboring code.
</p>

<p>
Basic formatting guidelines
</p>

<ul>
<li>3-space indentation, no tabs.
<li>Limit lines to 78 or fewer characters.  The idea is to prevent line
wrapping in 80-column editors and terminals.  There are exceptions, such
as if you're defining a large, static table of information.
<li>Opening braces go on the same line as the if/for/while statement.
For example:
<pre>
if (condition) {
   foo;
} else {
   bar;
}
</pre>

<li>Put a space before/after operators.  For example, <code>a = b + c;</code>
and not <code>a=b+c;</code>

<li>This GNU indent command generally does the right thing for formatting:
<pre>
indent -br -i3 -npcs --no-tabs infile.c -o outfile.c
</pre>

<li>
<p>Use comments wherever you think it would be helpful for other developers.
Several specific cases and style examples follow.  Note that we roughly
follow <a href="http://www.doxygen.nl">Doxygen</a> conventions.
</p>
Single-line comments:
<pre>
/* null-out pointer to prevent dangling reference below */
bufferObj = NULL;
</pre>
Or,
<pre>
bufferObj = NULL;  /* prevent dangling reference below */
</pre>
Multi-line comment:
<pre>
/* If this is a new buffer object id, or one which was generated but
 * never used before, allocate a buffer object now.
 */
</pre>
We try to quote the OpenGL specification where prudent:
<pre>
/* Page 38 of the PDF of the OpenGL ES 3.0 spec says:
 *
 *     "An INVALID_OPERATION error is generated for any of the following
 *     conditions:
 *
 *     * &lt;length&gt; is zero."
 *
 * Additionally, page 94 of the PDF of the OpenGL 4.5 core spec
 * (30.10.2014) also says this, so it's no longer allowed for desktop GL,
 * either.
 */
</pre>
Function comment example:
<pre>
/**
 * Create and initialize a new buffer object.  Called via the
 * ctx-&gt;Driver.CreateObject() driver callback function.
 * \param  name  integer name of the object
 * \param  type  one of GL_FOO, GL_BAR, etc.
 * \return  pointer to new object or NULL if error
 */
struct gl_object *
_mesa_create_object(GLuint name, GLenum type)
{
   /* function body */
}
</pre>

<li>Put the function return type and qualifiers on one line and the function
name and parameters on the next, as seen above.  This makes it easy to use
<code>grep ^function_name dir/*</code> to find function definitions.  Also,
the opening brace goes on the next line by itself (see above.)

<li>Function names follow various conventions depending on the type of function:
<pre>
glFooBar()       - a public GL entry point (in glapi_dispatch.c)
_mesa_FooBar()   - the internal immediate mode function
save_FooBar()    - retained mode (display list) function in dlist.c
foo_bar()        - a static (private) function
_mesa_foo_bar()  - an internal non-static Mesa function
</pre>

<li>Constants, macros and enum names are <code>ALL_UPPERCASE</code>, with _
between words.
<li>Mesa usually uses camel case for local variables (Ex:
<code>localVarname</code>) while gallium typically uses underscores (Ex:
<code>local_var_name</code>).
<li>Global variables are almost never used because Mesa should be thread-safe.

<li>Booleans.  Places that are not directly visible to the GL API
should prefer the use of <code>bool</code>, <code>true</code>, and
<code>false</code> over <code>GLboolean</code>, <code>GL_TRUE</code>, and
<code>GL_FALSE</code>.  In C code, this may mean that
<code>#include &lt;stdbool.h&gt;</code> needs to be added.  The
<code>try_emit_*</code> methods in <code>src/mesa/program/ir_to_mesa.cpp</code>
and <code>src/mesa/state_tracker/st_glsl_to_tgsi.cpp</code> can serve as
examples.

</ul>

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